Alternative Motifs for Halogen Bonding

The halogen‐bonding interaction is one of the rising stars in supramolecular chemistry. Although other weak interactions and their influence on the structure and chemistry of various molecules, complexes and materials have been investigated thoroughly, the field of halogen bonding is still quite unexplored and its impact on chemistry in general is yet to be fully revealed. In principle, every Y–X bond (Y = electron‐withdrawing atom or moiety, X = halogen atom) can act as a halogen‐bond donor when the halogen is polarized enough by Y. Perfluorohalocarbons are iconic halogen‐bond donor molecules in which Y is a perfluorinated aryl or alkyl moiety and X is either iodine or bromine. In this article, alternative halogen‐bond motifs such as X2···A and Ar–X···A [A = Lewis basic halogen‐bond‐accepting atom of a molecule or ion; Ar = neutral or charged (hetero)aromatic system] are reviewed. In addition, haloalkenes, haloalkynes, N‐haloamides and other non‐metallic halogen‐bond donors and their respective halogen‐bonded structures will also be described. Although purely organic halogen‐bonding motifs are very prominent, the role of metal complexes in halogen bonding is becoming increasingly evident as well, which is also reflected in this review. Finally, halogen bonding in solution is briefly highlighted. Contemporary research is proving that halogen bonding is more than a solid‐state phenomenon and is now a well‐recognized weak interaction in chemistry. Halogen bonding is an attractive non‐covalent interaction between an electrophilic halogen donor atom and a nucleophilic acceptor atom. The figure depicts halogen bonds between the electrophilic iodine atoms of four N‐iodosuccinimide (NIS) molecules and the nucleophilic nitrogen atoms of hexamethylenetetraamine (HMTA).